The present invention relates to an orthopedic prosthesis utilized in knee joint replacements. More particularly, the present invention is directed to a tibial implant system comprising a tibial insert and interchangeable tibial trays, one made of a metal and one made of a polymer.
Knee arthroplasty is a well-known surgical procedure to replace the weight-bearing surfaces of the knee joint to relieve pain and disability. It has enabled many individuals to function normally where it otherwise would be impossible. Artificial joints usually comprise metallic, ceramic, or plastic components implanted into existing bone.
In a typical procedure, a tibial tray or baseplate is mounted on a prepared proximal tibia of a patient and a tibial bearing insert is mounted on the tibial tray. Methods and corresponding tibial trays exist that allow for implantation into the tibia with or without the use of bone cement.
Earlier designs of tibial implant systems were typically composed primarily of metal trays or baseplates and bearings made of ultra-high-molecular-weight polyethylene (hereinafter “UHMWPE”). An earlier system, known as a monolithic UHMWPE device, comprised the bearing insert and bone-contacting portion as one piece implanted into the tibia through cement fixation. Although the system was resistant to stress shielding and had a long in vivo survival rate, the system fell out of favor with the medical industry because it was difficult to implant into the patient and because the bond between UHMWPE and bone with bone cement is not as strong as the bond with metal.
An improvement which is still currently used is a metal-backed UHMWPE modular tibia, which comprises a metal tray and a separate UHMWPE tibial insert. Although the two-part system made the device much easier to implant, the system was expensive.
Lastly, a system having a tibial tray composed of a polymer-porous metal composite has been recently developed for fixation without the need for bone cement, as can be seen in U.S. Pat. App. 2010/0100191, U.S. Pat. App. 2009/0084491, or U.S. Pat. App. 2011/0035018. Thus far, clinical results have shown that the cement-less bond is weaker than a bond using bone cement. In addition, devices comprising polymer-metal composites are expensive to manufacture.
Thus, there is a need for a modular tibial tray and insert system which can produce an improved, sustained bond with bone cement, reduces stress shielding, has improved resistance to fracture and wear, provides ease of use for surgeons, and be inexpensive to manufacture.
As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. The term “sagittal” refers to the plane dividing the body into left and right halves. The term “coronal” refers to the plane dividing the body into front and back halves.